Collapsing columns
From Joomla! Documentation
A common requirement when designing web pages in Joomla! is for a Module position to be removed when no Modules are enabled in that position so that the space is available for other page elements. The region removed is referred to as a "collapsed column." This can be achieved using the countModules function.
For example, if you want to include a user1 module position only if there are modules enabled in that position, you could use this code:
<?php if ($this->countModules( 'user1' )) : ?>
<div class="user1">
<jdoc:include type="modules" name="user1" style="xhtml" />
</div>
<?php endif; ?>
Notice that the <jdoc:include /> tag and its surrounding <div> are only included if the countModules call returns a non-zero value. (The PHP if statement treats zero as being false and any non-zero value as being true.)
Sometimes you may want a pair of module positions to collapse either singly or together.
<?php if ($this->countModules( 'user1 or user2' )) : ?>
<div class="user1user2">
<?php if ($this->countModules( 'user1' )) : ?>
<jdoc:include type="modules" name="user1" style="xhtml" />
<?php endif; ?>
<?php if ($this->countModules( 'user2' )) : ?>
<jdoc:include type="modules" name="user2" style="xhtml" />
<?php endif; ?>
</div>
<?php endif; ?>
Notice how the region (which is styled by the CSS class user1user2) is only output if either user1 or user2, or both, have at least one Module enabled.
If you want a divider to separate the two Module positions then you must be careful to only output the divider if both Module positions have Modules enabled in them. For example,
<?php if ($this->countModules( 'user1 or user2' )) : ?>
<div class="user1user2">
<?php if ($this->countModules( 'user1' )) : ?>
<jdoc:include type="modules" name="user1" style="xhtml" />
<?php endif; ?>
<?php if ($this->countModules( 'user1 and user2' )) : ?>
<div class="divider"></div>
<?php endif; ?>
<?php if ($this->countModules( 'user2' )) : ?>
<jdoc:include type="modules" name="user2" style="xhtml" />
<?php endif; ?>
</div>
<?php endif; ?>